Is the intent of this that the prototype is made during this jam period, or are you also accepting games that were already being actively developed and would be a good fit for the theme?

Ideally you'd create a prototype during this jam period and submit it before submissions close. As long as your game meets the requirements, theme included, it'll be considered.

Jumping in - you can create something from scratch or use an existing game. Only requirements are that you have have the rights to everything you use and that it works with our Unity SDK! https://docs.spatial.io/